A. Field of the Invention
The field of the present invention relates generally to systems for controlling sediment in earthen basins, such as groundwater recharge and flood control basins. More specifically, the present invention relates to such systems that utilize multiple sloped surfaces through which fluid can continually percolate so as to prevent sediments that would otherwise impede the flow of the fluid through the earthen basin.
B. Background Art
Earthen basins are commonly used to contain water for several purposes including, but not limited to, groundwater recharge of surface water, flood control and containment of municipal, industrial and agricultural waste waters. The function of these basins often rely on, or are enhanced by, the percolation of the contained water through the bottom and sides of the basin. The percolation rate of the basin is primarily controlled by the underlying soil conditions and material and by the amount and type of sediment which has settled on the surface of the basin bottom. The sediment usually becomes the controlling element, often clogging a basin so that pumping the water or fluid from the basin becomes the only economical means of draining the basin for maintenance. The subsequent removal or mixing of this clogging sediment requires light and/or heavy equipment after the basin has adequately dried. The equipment used for basin maintenance can compact the surface material, thereby requiring additional efforts to uncompact the material and return the basin to its maximum infiltration performance levels. The challenge for basin designers and operators has been to develop a low maintenance facility without compromising percolation effectiveness.
It is well known that percolation is at or near the maximum rate for the first several months of operation after initial basin construction or after maintenance of an existing basin because the surface of the basin has not had time to become clogged by sediment materials. The surface clogging sediment results from several sources of fines, including single cell and filamentous algae, silts and clays in the irrigation/recharge water and generated by interbasin erosion (filling and levy erosion. Over time the percolation ability of the basin decreases as the sediment forms a virtually non-impregnable clogging layer. The infiltration clogging effect of the sediment is a serious concern for all industries, businesses and agencies using percolation basins. Accumulated sediments limit the percolation of water through a basin and, without routine mechanical maintenance, the clogging effect will eventually render a basin""s percolation ability virtually useless. As explained in more detail below, basin owners and operators have historically used discing, ripping, scraping and combinations thereof to control and/or remove the clogging sediment layer with varying degrees of success. If the sediment was composed of inorganic material, discing or shallow mixing is often ineffective because the near surface becomes clogged with the accumulated fine grained material. If the sediment included sufficient organic material, discing or shallow mixing without routine deep drying cycles is ineffective because the near surface becomes clogged with anaerobic microbes. Scraping and subsequent ripping can be effective, but it is costly and is typically required at least every three years.
Sediments are inorganic and/or organic particles which settle on the surface of the basin during the filling and operation of the basin. The sediments are generated and accumulated via several mechanisms including: (1) release of silt and clay from the native basin material into suspension by turbulence from the filling water in a freshly maintained or newly constructed basin; (2) wave action on the basin""s perimeter side slopes; (3) settling of the suspended silt and clay contained in the influent water; and (4) settling of suspended organic materials (i.e., algae and weeds) that grow in the basin. Clays and silt-clays (fines) are deposited as a thin layer on the bottom of the basins. A layer of these fines as thin as one-eighth inch has about as much resistance to infiltration as two feet of silty sands, forty feet of sugar sands and two thousand feet of clean gravel. Over time, organics may also settle to the bottom of the basin. These settled organics also affect the infiltration ability of the basin.
The common methods of maintaining the basin and controlling the clogging effect are expensive and time consuming. All these methods first require that the basin be drained and dried. After drying, heavy equipment is normally used to access and work in the basin""s bottom. The draining process sometimes requires pumping the water from the basin when the basin""s bottom is significantly clogged. Pumping is also used when the basin""s bottom is only somewhat clogged, but time is of the essence. Set forth below is a summary of the various maintenance methods that are used (after first draining the basin).
The xe2x80x9cDry and Crackxe2x80x9d Method (also referred to as the xe2x80x9cChipxe2x80x9d Method) is often used where the climate is normally hot and dry and the water availability is intermittent or sporadic. It is also used where land for basin construction is abundant and basins can be easily cycled in and out of operation. The surface sediment on the bottom of the basin is allowed to dry and crack to form what are commonly known as xe2x80x9cchips,xe2x80x9d due to their appearance similarity to potato chips. Once the chips are formed, the basin is generally brought into operation without any mechanical cleaning. Although the permeability of the basin is initially substantially improved, the chips soon resettle and the small spaces between the chips are soon filled with sediment and the basin becomes clogged, requiring the basin to be re-dried. This process is repeated frequently, sometimes as often as twice a month. Periodically, the chips have to be removed by mechanical scraping or raking. The material just under the surface normally becomes compacted, further restricting percolation. Under this method, the operational time of the basin is limited to relatively short periods between refilling of the basin and stopping the influent flow to allow drying. As is well known, the effectiveness of the Chip Method is limited by climate, water availability and available land for multiple basins.
The xe2x80x9cShallow Mixxe2x80x9d Method is the desired method when the climate facilitates faster basin drying and time is of the essence for basin maintenance. It is also used when and/or where removal of the sediment is difficult or where the concentration of sediment in the influent water is relatively high, thereby making the Chip Method less viable. The basin bottom is dried longer and deeper than in the Chip Method, forming chips and a moisture content that will allow mechanical equipment, such as a tractor, to drive on the bottom and use a tool, such as a disc, spring tooth, plow or other shallow mixing device, to break-up and mix the chips with the upper surface material. The chips and/or sediments are mixed with the upper surface material to disperse the thin layer of clogging sediment into the upper surface material. The mixing usually takes place within the upper six inches or fifteen centimeters of the basin bottom. This method is more effective than the Chip Method at dispersing the layer of sediment and temporarily improving the permeability of the basin. This process is repeated as needed, typically once a year. Depending on the soil composition and the amount of compaction from the tractor, occasional ripping may be needed to maintain acceptable percolation rates. With repeated mixing of inorganic sediment, the mixed layer becomes increasingly impermeable and must eventually be removed. If the repeated mixing includes the presence of organic sediments, the mixed layer will likely support an active anaerobic condition when the basin is in operation. Anaerobic microbes develop and thrive in oxygen poor environments and in the presence of organic nutrients. Over time, the slime-bodied anaerobic microbes become the clogging layer and limit the percolation rate.
The maintenance of an inorganic or anaerobic clogged basin requires the basin be dried to a level where heavy equipment, such as a paddle wheel scraper, is used to remove a minimum of six inches or fifteen centimeters of material. Unfortunately, the use of heavy wheeled equipment, including the paddle wheel scraper, compacts the upper portion of the basin""s bottom. This compaction is so detrimental to percolation that it is often necessary and/or cost effective to then utilize another piece of heavy equipment, for instance a tracklayer (bulldozer) with ripping shanks to decompact or loosen the compacted upper layer. A slip plow is often used in conjunction with the ripping shanks to provide the most effective ripping operation. Although generally beneficial, the ripping operation can bring stones or unwanted pieces of cemented material to the surface. Ripping also leaves the ground surface so uneven that yet another piece of equipment, such as a tractor and disc or springtooth, is sometimes used to provide a more even basin bottom surface. The basin is then filled for normal operation. Although this method provides better conditions for long term percolation than does the Chip Method, the cost of routine mixing, eventual material removal and compaction ripping is significant. As a result, the Shallow Mix Method is limited by the availability and cost of operating heavy equipment. The effectiveness of this method is also limited by climate, water availability and loss of basin operation benefits due to the time needed for adequate drying and equipment operation.
A third method, the xe2x80x9cDeep Mixingxe2x80x9d Method, is the desired method when the influent water""s sediment concentration is quite high and removal of the sediment is difficult. This method is also used when the sediment is difficult to dry and/or remove or when it can be mixed in the underlying material with available heavy equipment. In this method, the basin bottom is dried to a moisture content that allows heavy equipment, such as a tracklayer, to drive on the bottom and use a ripping shank, perhaps combined with a slip plow, or other deep mixing device. The surface chips and/or thin sediment layers are mixed with the underlying material to disperse the clogging sediment into the underlying material. This mixing usually takes place within the upper six feet or two meters. This method is also effective at dispersing the layer of sediment and temporarily improving the permeability of the basin. The mixing process is repeated as needed, normally once a year or less often as conditions require.
With repeated mixing and the presence of organic sediment, as commonly found in municipal waste water treatment effluent ponding basins, the deeply mixed layer will likely begin to support an active anaerobic condition. This anaerobic condition will likely occur and continue even when the basin is drained and not in operation since most of the mixed organics are at depths that rarely dry. Over time, the slime-bodied anaerobic microbes themselves will become the clogging layer and limit the percolation rate. The eventual maintenance of an anaerobic clogged basin requires the basin be dried to a level where very heavy equipment, such as a paddle wheel scraper, can be used to remove all the organically clogged material. This scraping operation requires large amounts of earthen material to be stockpiled or removed from the basin area.
As with the Shallow Mixing Method, the use of heavy wheeled scraping equipment, such as a paddle wheel scraper, normally compacts the upper portion of the scraped basin bottom. As with any scraping operation the resultant compaction is detrimental to the percolation and should be dealt with as described above. The basin is then ready for filling and normal operation. This method provides better conditions for long term percolation than does the Chip or Shallow Mixing Methods. The cost of routine mixing and the eventual removal of large quantities of material and compaction ripping, however, makes the Deep Mixing Method a very expensive means of maintaining a water containment basin and creates long term constraints. This method is significantly limited by the availability and cost of operating heavy equipment and disposal of the unwanted material. The effectiveness of this method is also limited by climate, water availability and loss of basin operation benefits due to the time needed for adequate drying and equipment operation.
Growing concerns regarding contaminants (i.e., regulated chemicals and substances) leaching into the groundwater from percolation basins has resulted in new regulations regarding the control of erosion at construction sites where surface drainage waters flow into the basins. As is well known, eroded sediments will often adsorb or bond to common contaminants and then carry those contaminants into the containment basin. In general, the prior art Chip, Shallow Mixing and Deep Mixing methods of basin maintenance are poor methods of contaminant control because the contaminants remain in the bottom of the basin where percolation is taking place. In fact, these three methods are somewhat in conflict with contaminant control goals because the contaminants can be easily leached, with the percolating water into the unsaturated or vadose zone, then possibly into the groundwater. When contaminant control is also required of a basin, basin maintenance becomes increasingly important and more expensive. The frequently required basin draining, drying, removal of sediments and contaminants followed by the efforts to decompact the soil require significant downtime, staff and equipment. In addition, there are concerns with air dispersal of sediments and contaminants during the basin maintenance process by the creation of dust and dust particles. The conflict of percolation effectiveness versus contaminant management usually results in basins having less effective percolation characteristics and utilizing basin maintenance methods that maintain those characteristics. Concerns regarding sediment as a basin contaminant have recently required building contractors to employ expensive on-the-jobsite sediment and other contaminant containment practices and equipment.
One such method that is used for management of contaminants is the xe2x80x9cMinimum Scrapingxe2x80x9d Method. This method is employed when the object of the maintenance is to remove the sediment with the minimum amount of excess (i.e., disposal) material, such as when the sediment is considered to contain contaminants that could accumulate over time and become hazardous waste or result in groundwater contamination. This Minimum Scraping Method is used by some urban flood control agencies who operate basins with fixed infrastructure improvements (explained below), need to minimize contaminant accumulation and want to minimize the excavation of the basin bottom. Basins sometimes have infrastructure, such as dewatering pumps and inlet structures, which are typically placed at the lowest elevation of the basin bottom to facilitate the removal of water from the basin. These structures become less effective as repeated scraping and removal of basin material results in the basin bottom being placed below the fixed structures. The routine removal of excess material from the basin deepens it beyond a desired depth. As a result of these significant concerns, the basin bottom is not ripped or decompacted then disked or somewhat flattened after the sediment is removed. To do so, would result in the creation of an uneven bottom surface requiring subsequent removal of the excess material during the following cleaning. Consequently, the basin bottom becomes increasingly compacted and less permeable over time.
To maintain the basin, the basin bottom is dried sufficiently to allow equipment, such as a motor grader, to drive on the bottom and windrow the thin layer of sediment into ridges. The windrowed sediments are welted (to limit air dispersal) then scraped up by a loader into a dump truck, or similar equipment, for removal. This process leaves the basin bottom relatively smooth and flat and is repeated as needed. Depending on the soil composition and the amount of compaction from the equipment, the basin bottom usually becomes compacted quickly, resulting in ever decreasing percolation rates between cleanings. The basin is then ready for filling and normal operation. The Minimum Scraping method serves it""s prime objective of removing the sediment and most contaminants. However, the resulting compaction significantly degrades the percolation ability of the basin. This usually results in the basin having to be drained by pumping rather than by percolation. This method is limited by the availability and cost of operating pumping and heavy equipment. The effectiveness of this method is also limited by climate, water availability and loss of basin operation benefits due to the time needed for adequate draining/pumping/drying and equipment operation.
What is needed is an improved system for controlling sediment in fluid containment basins that is beneficial for both effective percolation rates and management of contaminants. Such an improved system should reduce the frequency of basin maintenance, the cost of that maintenance and the need to dispose of unwanted basin materials. In addition, an improved sediment control system should be cost effective for installation in new fluid containment basins and easily adaptable to existing water containment basins. Ideally, an improved sediment control system should minimize the amount of labor necessary for basin maintenance, the amount and frequency of basin downtime and the air dispersal of any basin contaminants.
The sediment control system for fluid containment basins of the present invention provides the benefits and solves the problems identified above. That is to say, the present invention discloses a sediment control system that reduces the clogging effect of sediments found in basin influent and, thereby, reduces the need for basin maintenance. Use of the system of the present invention reduces the frequency and cost of basin maintenance, the amount of labor and materials needed for maintenance, the need to dispose of unwanted basin materials and the amount of time a basin must be taken out of operation for maintenance. The system of the present invention also reduces the likelihood that contaminants will be dispersed in the air. The sediment control system is easy and cost effective for both new fluid containment basins and retrofitting of existing fluid containment basins. In addition, the system of the present invention can be used for fluid containment systems that are configured to contain and percolate fluids other than water and which percolate that fluid through mediums other than just soils.
In one embodiment of the present invention, the sediment control system for fluid containment basins comprises a fluid containment basin that is configured to receive and store a volume of fluid, such as water, therein. The typical basin is formed by a plurality of basin embankments enclosing a basin bottom. One or more ridges are placed on the basin bottom in the basin. Each of the ridges generally have at least two sides and an upper area at and near the top of the ridge. The sides formed at a sloped angle sufficient to facilitate the operation of the present invention. Next to the ridges are located furrows that are formed substantially parallel to the ridges. In the preferred embodiment, the basin contains a plurality of ridges and a plurality of furrows. The ridges form at least one pair of spaced apart ridges with a furrow disposed between and bounded by the pair of ridges. Preferably, the plurality of ridges are generally parallel to each other and to at least one of the basin""s embankments. The ridges should be shaped and configured, such as an inverted xe2x80x9cVxe2x80x9d shape, to facilitate the settlement of sediment contained in the fluid into the one or more furrows. The ridges can be formed from material that is taken from the bottom of the basin used to form the furrows or it can be brought into the basin from an outside source. When properly constructed, at least a portion of the upper area and the sides of the ridges are washed relatively clean of sediment (which settled out of the fluid when it was at a level above the ridges) by the wave action against the ridges. Although the use of wind to generate the waves is preferred, the basin can comprise a mechanism for generating the waves.
The present invention also includes a method of establishing a fluid containment basin that is configured to receive and store a volume of fluid in the basin. As above, the standard basin has a plurality of basin embankments enclosing a basin bottom. The method adds the steps of forming ridges on the bottom of the basin where each of the ridges has at least two sides and an upper area. Also formed in the basin bottom are furrows. The furrows should be formed adjacent to the ridges. The basin should then be filled with fluid such that W the level of the fluid in the basin is above the ridges. Again, the ridges should be shaped and configured to facilitate the settlement of sediment contained in the fluid into the furrows positioned in between the ridges. The furrows can be made into or comprise an impermeable layer to prevent contaminants that may be in the fluid from leaching out of the basin through the furrows.
The present invention also includes a method for enhancing the permeability of and/or providing for the collection of sediment in a fluid containment basin having the steps of forming the furrows, forming the ridges adjacent to the furrows and filling the basin with fluid to submerge the ridges. To maintain permeability the flow of fluid into the basin should be reduced on a periodic basis so that wave action can wash sediment off of the upper area and sides of the ridges as the water level is lowered. After washing of the ridges, the basin can be re-filled with fluid. In an alternative embodiment, a substantially impermeable mat of sediment can be allowed to form in the furrows to prevent migration of one or more contaminants contained in the fluid out of the basin. With the contaminants contained in the furrows, they can be treated or, if sufficient time is available, allowed to deteriorate into harmless or less harmful components.
Accordingly, the primary objective of the present invention is to provide a sediment control system for water containment basins having the features generally described above and more specifically described below in the detailed description.
It is also an important objective of the present invention to provide a sediment control system for water containment basins that results in easily maintained, permeable sloped surfaces (ridges) through which water percolates without the clogging restrictions at the bottom of the basin between ridges.
It is also an important objective of the present invention to provide a sediment control system for water containment basins that minimizes the potential for groundwater contamination from sediment which may be bonded with contaminants by collecting such sediments in the portion of the basin where the least amount of percolation takes place.
It is also an important objective of the present invention to provide a sediment control system for water containment basins that has relatively easily maintainable areas in the bottom of the basin furrows.
It is also an important objective of the present invention to provide a sediment control system for water containment basins that primarily uses naturally occurring forces, such as wind and gravity, to provide basin maintenance, thereby minimizing the use of fossil fuels and reducing pollution.
It is also an important objective of the present invention to provide a sediment control system for water containment basins that is cost effective to install and maintain for both new basin installations and the retrofitting of existing basins.
The above and other objectives of the present invention will be explained in greater detail by reference to the attached figures and the description of the preferred embodiment which follows. As set forth herein, the present invention resides in the novel features of form, construction, mode of operation and combination of parts presently described and understood by the claims.